1. Field of the Invention
The present invention relates to an on-demand type ink-jet printer for effecting a direct recording by jetting ink droplets on a recording medium, particularly to an on-demand type ink-jet printer having an improved deflection system for deflecting ink droplets jetting from an on-demand type ink-jet print head.
2. Description of the Prior Art
In a conventional ink-jet printer, an electrostatic deflection method is used for deflecting a flying ink droplet. A system utilizing such a method deflects the droplet along a deflecting electric field created by a pair of deflecting electrodes which are placed along, and to the side, of charged ink droplets. Such a system is disadvantageous in that it is required to enlarge a distance between an ink jet nozzle and a recording medium so that the deflecting electrodes can be inserted therebetween.
On the other hand, a so-called on-demand type ink-jet recording printer is also well known and has been used for a printer, facsimile equipment and the like. The ink-jet printer of the on-demand type is described in detail, for example, in the U.S. Pat. No. 3,946,398 entitled "METHOD AND APPARATUS FOR RECORDING WITH WRITING FLUIDS AND DROP PROJECTION MEANS THEREFOR" issued to E. L. Kyser et al.
In the on-demand type ink-jet printer, the velocities of the flying ink droplets are relatively slow and, when an interval between the formation of ink droplets is varied, properties such as the flying velocities and the volumes of the ink drops are largely varied also. Therefore, to record an undistorted picture, it is necessary to reduce the distance between the nozzle and the recording medium as small as possible. Consequently, it is difficult to record the picture with an excellent picture quality by using the electrostatic deflection electrodes on the on-demand type ink-jet system. Moreover, in case where a multi-nozzle head is constructed by integrating plural nozzles, it is extremely difficult in respect to the structure of the apparatus and the electrical insulation to arrange plural deflecting electrodes corresponding to the plural nozzles in a minute space.
In addition, when a repetition frequency of the ink droplets is varied in response to the picture signal, the flying velocities thereof is also varied. If the electrostatic deflection is carried out in this situation, it is extremely difficult to precisely control the deflection only by the deflection electric field, because the deflection angle is inversely proportional to the flying velocity of the ink droplet, so that the former is varied in response to the variation of the latter.
It is, therefore, an object of the present invention to provide an on-demand type ink-jet printer having a simplified deflection system.